Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Near critical temperature of refrigerant

Much below critical temperature

Above critical temperature

2. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Equally

Less

3. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

4. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Reversed Rankine

Rankine

Carnot

5. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.6

0.376

0.4

6. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

7. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

High risibility with oil

Large latent heat

Low boiling point

8. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Absorber

Condenser, absorber and separator (rectifier)

Evaporator

9. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

1.25

2.15

10. Critical temperature is the temperature above which

Water will evaporate

A gas will immediately liquefy

Water will never evaporate

A gas will never liquefy

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11. The boiling point of ammonia is

-10.5°C

-33.3°C

-77.7°C

-30°C

12. The domestic refrigerator uses following type of compressor

Axial

Miniature sealed unit

Piston type reciprocating

Centrifugal

13. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

None of these

Positive

Zero

14. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Involves no change in volume

Takes place at constant entropy

Takes place at constant pressure

15. Most thermostatic expansion valves are set for a superheat of

20°C

10°C

15°C

5°C

16. The operating pressure for refrigerating units using R-12 as a refrigerant is

2 bar

30 bar

8 bar

15 bar

17. A bootstrap air cooling system has

Three heat exchangers

Two heat exchangers

Four heat exchangers

One heat exchanger

18. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Condenser tubes

Evaporator tubes

Refrigerant cooling tubes

19. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

9: 1

1: 1

1: 9

1: 3

20. The minimum temperature to which water can be cooled in a cooling tower is

Dry bulb temperature of air

Wet bulb temperature of air

Ambient air temperature

Dew point temperature of air

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21. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Evaporator and compressor

Receiver and evaporator

Condenser and receiver

22. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

2.33

1.33

4.33

23. Which of the following statement is correct?

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

24. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

25. The freezing point of sulphur dioxide is

-135.8°C

-56.6°C

-75.2°C

-77.7°C

26. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Equal to unity

Any one of the above

Always less than unity

27. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

None of the above

28. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

None of these

Sub-cooling or under-cooling

Super-cooling

Normal cooling

29. Which of the following cycles uses air as the refrigerant?

Carnot

Stirling

Ericson

Bell Coleman

30. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Freon

Carbon dioxide

Ammonia

Page 4 of 4

31. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

32. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

33. In a lithium bromide absorption refrigeration system

None of these

Water is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

34. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Collect vapours

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

35. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

36. Freon group of refrigerants are

Toxic

Nontoxic and non-inflammable

Non-inflammable and toxic

Inflammable

37. The capillary tube, as an expansion device, is used in

All of these

Water coolers

Domestic refrigerators

Room air conditioners

38. For obtaining high COP, the pressure range of compressor should be

High

Low

Optimum

Any value

39. The curved lines on a psychrometric chart indicates

Dew point temperature

Dry bulb temperature

Wet bulb temperature

Relative humidity

40. Rating of a domestic refrigerator is of the order of

10 tons

40 tons

0.1 ton

5 tons

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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